1. Field of the Invention
The present invention relates to an antiglare film to be provided on the surface of a window, display etc. In particular, it relates to an antiglare film to be provided on the surface of such displays as a liquid crystal display (LCD), cathode-ray tube (CRT) display, plasma display (PDP), organic electroluminescence display (ELD) and field effect display (FED, SED).
2. Description of the Related Art
Displays such as a liquid crystal display, CRT display, EL display and plasma display have the following problems from the viewpoint of visibility:
External light reflects at looking and listening.
Surface glare (scintillation) occurs at the display surface by display light from the display.
Poor visibility caused by dazzle of display light directly coming from the display without being diffused, etc.
Visibility is also degraded by such defect as unevenness of brightness.
In order to solve such lowering or degradation of visibility, it is known to arrange an antiglare film with an uneven surface on the front face of a display.
As an antiglare film, for example, the following techniques are known:
To arrange, on the surface of a display, an antiglare film having an antiglare light diffusing layer having been subjected to embossing finish.
To arrange, on the surface of a display, an antiglare film having an antiglare light diffusing layer on the surface of which is formed irregularity by mixing particles in a binder matrix.
In such antiglare film, scattering phenomenon (surface diffusion) of light caused by surface irregularity is utilized.
Further, such antiglare film is also known that, by mixing particles having a refraction index different from that of a binder matrix into the binder matrix, utilizes internal scattering (internal diffusion) of light based on the difference in refraction indices of the binder matrix and particles.
In an antiglare film on the surface of which is formed irregularity through embossing finish, the surface irregularity thereof can be completely controlled. Consequently, reproducibility is good. However, when there is a defect or an adhered foreign substance on an emboss roll, endless defects occurs at the pitch of roll. Consequently, in the case of mass production, all the products have defect. Further, since the scattering only at the surface is utilized, there are following problems:
Abrasion resistance
Lowering of contrast
Occurrence of dazzling
An antiglare film using a binder matrix and particles can be manufactured through a smaller number of processes than the antiglare film using embossing finish. Accordingly, it can be manufactured inexpensively. Therefore, various embodiments of antiglare film are known (Patent Document 1).
For example, following antiglare films are known.
It is necessary to improve visibility by preventing reflection of external light, scintillation etc. Therefore, following methods have been considered:
To improve light diffusing performance by making irregularity figure of the surface large.
To improve light diffusing performance by increasing the amount of particles to be added.
However, there is such problem in the methods that the sharpness of a transmitted image is lowered.
As methods for improving the visibility etc. without lowering light diffusing performance and the like, following techniques are known:
A technique in which binder matrix resin, spherical particles and amorphous particles are used in combination (Patent Document 2).
A technique in which binder matrix resin and plural particles having different particle sizes are used (Patent Document 3).
A technique including surface irregularity, wherein the cross-sectional area of the concave portion is defined (Patent Document 4).
In addition, in order to improve the visibility without lowering light diffusing performance etc., there is also known such technique that uses scattering in an antiglare film and scattering at the surface of antiglare film in combination.
The scattering within an antiglare film (internal diffusion) occurs by dispersing particles in a binder matrix such as resin of an antiglare film, the particles having refraction index different from that of the binder matrix. In order to exert sufficient light diffusing performance, it is necessary to form a certain degree of surface irregularity on the surface of antiglare film. However, there are following problems:
Lowering of contrast
Occurrence of dazzling caused by lens effect of the surface irregularity
Lowering of abrasion resistance
The combined use of internal scattering and surface scattering leads to smaller surface irregularity compared with an antiglare film using surface scattering alone. Therefore, there are following advantages:
Improvement of contrast
Reduction of dazzling caused by lens effect of the surface irregularity
Improvement of abrasion resistance
For example, as the technique using internal scattering and surface scattering in combination, following techniques are known:
A technique wherein the internal haze (cloudiness) is 1-15%, and the surface haze (cloudiness) is 7-30% (Patent Documents 5, 6).
A technique wherein, while using binder resin and particles having the particle size of 0.5-5 μm, the difference in refraction indices of the resin and the particle is 0.02-0.2 (Patent Document 7).
A technique wherein, while using binder resin and particles having the particle size of 1-5 μm, the difference in refraction indices of the resin and the particle is 0.05-0.15. Further, techniques defining a solvent to be used, surface roughness etc. (Patent Documents 8, 9, 10, 11, 12).
A technique wherein, using binder resin and plural types of particles, the difference in refraction indices of the resin and the particle is 0.03-0.2 (Patent Documents 13, 14).
There are also known following techniques that reduce lowering of contrast, hue variation etc. when a viewing angle is altered. In the technique, the surface haze (cloudiness) is 3 or more. Further, the difference between the haze value in the direction of normal line and the haze value in the direction of ±60° is 4 or less (Patent Documents 15, 16, 17, 18). A technique wherein center line average roughness (Ra) is 0.2 μm or less is also known (Patent Document 19). A technique wherein the center line average roughness (Ra) is 0.02-1 μm, and the ten point average roughness (Rz)/Ra is 30 or less is also known (Patent Document 20, 21).
Since an antiglare film is mainly arranged on the front face of a display, abrasion resistance is required. In order to improve the abrasion resistance, it is necessary to improve the hardness of an antiglare film. Therefore, there is known such technique as using an ionizing radiation-curing resin binder, silica particles and silicone particles in order to manufacture an antiglare film having a high hardness without lowering the display image quality of a display (Patent Document 21).
As described above, there are disclosed antiglare films of various constitutions for various purposes.
The performance required for an antiglare film differs depending on displays when it is used on the front face of a display. For example, the optimum antiglare film differs depending on the resolving power of a display, intended purpose etc. A broad range of antiglare films are required according to intended purposes.
Since an antiglare film has an antiglare layer of which surface has concaves and convexes, the film can scatter light and prevent external light from reflecting. However, in a case where the size of the concaves and convexes was increased in order to improve external light reflection preventive properties, the antiglare layer of the antiglare film was whitened. Since the external light preventive properties and the whitening degree were in a trade-off relation, it was difficult to obtain an antiglare film having high external light reflection preventive properties without the whitening. A purpose of the present invention, among others as will be evident to those skilled in the art, is to provide an antiglare film which is superior in external light reflection preventive properties without the whitening.
[Patent Document 1] U.S. Pat. No. 5,387,463
[Patent Document 2] JP-A-2003-260748
[Patent Document 3] JP-A-2004-004777
[Patent Document 4] JP-A-2003-004903
[Patent Document 5] Japanese Patent No. 3507719
[Patent Document 6] U.S. Pat. No. 6,343,865
[Patent Document 7] JP-A-11-326608
[Patent Document 8] Japanese Patent No. 3515426
[Patent Document 9] U.S. Pat. No. 6,696,140
[Patent Document 10] U.S. Pat. No. 7,033,638
[Patent Document 11] US Patent Published Application No. 2002-0150722
[Patent Document 12] US Patent Published Application No. 2004-0150874
[Patent Document 13] Japanese Patent No. 3515401
[Patent Document 14] U.S. Pat. No. 6,217,176
[Patent Document 15] JP-A-11-160505
[Patent Document 16] U.S. Pat. No. 6,111,699
[Patent Document 17] U.S. Pat. No. 6,327,088
[Patent Document 18] U.S. Pat. No. 6,480,249
[Patent Document 19] JP-A-2003-149413
[Patent Document 20] JP-A-2004-125958
[Patent Document 21] JP-A-2004-082613
[Patent Document 22] US Patent Published Application No. 2004-0071986